CHICAGO (Reuters) - A study of rapid influenza tests found they miss many cases of swine flu and U.S. health experts said on Thursday they are not worth the trouble for this flu season.

A study looking at the effectiveness of a rapid flu test in the first few weeks of the H1N1 pandemic in May found it detected less than half of the cases later confirmed by more sophisticated tests.

The findings, which appeared in the U.S. Centers for Disease Control and Prevention's weekly report on death and disease, confirm the CDC's current guidelines, which stress that people with flu-like symptoms should get quick treatment, before getting a flu test.

Health and Human Services Secretary Kathleen Sebelius told reporters at a briefing that doctors should simply treat symptoms and not bother with testing.

"The flu is the flu is the flu," she said.

In September, the CDC said doctors should not wait for laboratory confirmation of H1N1 because quick treatment is important, and because a negative rapid test does not rule out the flu.

The latest study, conducted by Dr. James Sabetta and colleagues at the Greenwich Hospital and the Greenwich Department of Health in Connecticut, shows why.

They collected data on patients from two school outbreaks of pandemic H1N1 flu in May. They did rapid flu diagnostic tests on 63 patients using the Xpect Flu A&B test by Remel, a unit of Thermo Fisher Scientific, and more sophisticated lab tests.

They found the rapid flu test detected just 47 percent of the pandemic flu cases later confirmed by a slower, but highly accurate test called real-time reverse transcription-polymerase chain reaction, or rRT-PCR, which checks for the genetic material of the virus.

The findings confirm an earlier study by the CDC that found quick flu tests caught just 40 to 69 percent of swine flu cases. That study, released in August, looked at three popular flu tests -- BinaxNow, made by Inverness Medical Innovations, Becton Dickinson's Directigen EZ Flu A+B test and Quidel's QuickVue.

The CDC said the findings confirm their current guidelines, and stress that treating flu -- whether seasonal or pandemic -- is more important than knowing what kind a person has.

"Almost everybody will almost certainly not know what kind of flu they had," Dr. Anne Schuchat of the CDC told the briefing.

Many companies are working on better rapid tests including GlaxoSmithKline and Enigma Diagnostics, Seegene, a company based in South Korea and Maryland, DxNA based in Utah, and Osmetech PLC, based in California.